1. Field of the Invention
The present invention relates to a track access control system for use in a disk system, for example, an optical disk system, or a magnetic disk system, to enable the light beam from a head to follow a disk track. More particularly, it relates to a track access control system having an eccentricity (or offset) correction means which can be formed by a circuit of simple construction.
2. Description of the Related Art
Recently, optical disk units have attracted public attention as useful as a large capacity memory unit, since the track pitch can be made a few microns, and because a light beam can be used to read and write data from and to the optical disk.
This optical disk unit employs a track servo controller for enabling a light beam (light spot) to follow an optical disk track.
In this track servo control system, diffraction by a pre-groove in an optical disk, used as a recording medium, is utilized to generate a track error signal based on which servo control is utilized to enable a light spot to follow a track (guide groove) in the optical disk.
Because non-contact recording/reproduction can be carried out, the optical disk used in many optical disk units is a replaceable type, however a replaceable optical disk is frequently decentered or offcentered and a long time is required for a pull-in of the track servo. Accordingly, eccentricity correction control has been adopted (Re: NIKKEI MECHANICAL 1987, 7, 13. PP. 73-74). The eccentricity correction control, as described hereinafter, however, has the defects of complex circuit construction and low accuracy.